Effectiveness of biochar- And boron-coated diammonium phosphate for improving boron availability to sunflower (Helianthus annuus)

Sunflower (Helianthus annuus L.) growth and yield are severely compromised by boron (B) deficiency in alkaline calcareous soils of Pakistan. Biochar produced through low-temperature pyrolysis helps to maintain acidic functional groups in such soils. The aim of this study was to enhance B availability in biochar-amended alkaline calcareous soils in order to improve morpho-physiological and yield attributes of sunflower. In a pot experiment, sunflower was grown with three fertiliser treatments: Diammonium phosphate (DAP) alone; simple B + DAP; and DAP coated with biochar and B (BC-BDAP). All treatments were grown in soil receiving no biochar, and the BC-BDAP treatment was also applied in soil amended with wheat straw biochar at 2% and 4%. Preparation with wheat straw biochar improved soil properties such that soil with 4% biochar showed highest levels of organic matter (0.97%), total nitrogen (0.08%), available phosphorus (6.21 mg/kg), extractable potassium (93.4 mg/kg) and available B (0.41 mg/kg). Furthermore, compared with DAP alone and B + DAP, BC-BDAP in 4% biochar-amended soil enhanced the concentrations of shoot B (by 64% and 35%) and root B (by 41% and 26%), respectively. This indicated sufficient B availability in soil for root absorption, which subsequently increased sunflower achene weight per plant (by 33% and 17%), protein content (by 29% and 18%) and oil content (by 17% and 10%). Thus, application of BC-BDAP fertiliser in 4% biochar-amended soil can be an efficient strategy for enhancing B availability in alkaline calcareous soils and increasing sunflower growth and yield.